Method for electrolytic deposition of indium, and bath therefor



Patented Oct. 26, 1948 UNITED STATES "OFFICE METHOD FOR ELEo'moLYric DEPOSITION 0F INDTUM, AND BATH THEREFOR John Robert Dyer, Jr., Utica, N. Y., assignor to The Indium Corporation of America, New York, N. Y., a corporation of New York No Drawing. Application March 123.1945, r1 Serial No. 584,495 r 4 Claims. (01.56445) This invention relates to the electrolytic deposition of metal, to electrolytic baths and (accompositions of matter useful therein.

Although the art of electrodeposi-tion of metals has been highly developed and has been the subject of extensive research, the practical processes of electroplating and electro-refining have, in general, utilized either aqueous solutions or fused baths. The electroplating of indium, in particular, has, in the past, .been achieved with aqueous an entirely different type of plating bath, namely,

a non-aqueous bath, using as the solvent an organic liquid of the type known in physical chemistry a associating" solvent, having a high dielectric constant and low molecular weight. Thus, in the electroplating of indium, I have found the lower amides and especially formamide extraordinarily advantageous. These amides are somewhat amphoteric in their nature, exhibiting weal: basic properties due to the NHz group and weak acid properties due to the acyl group RC0, and it is probable that the advantageous properties of th indium formamide plating bath is, in part, due to this characteristic of the formamide, although the reactions which take place when the indium compound is added to the formamide are not as yet certainly identified.

As one example of my invention, indium hydroxide can be dissolved in formamide in the proportion of 21 grams per liter and this solution used, with or without addition agents, for the plating of indium. Using a pure indium anode, a, current density of amperes per sq. foot and a voltage of 6 to 9 volts, this bath showed an anode efficiency of 100% and a cathode efiiciency of 95% and a deposition of 21 to 24 milligram per ampere/minute. The bath shows an excellent throwing power such that it is particularly useful for plating of castings or overplating of other electrodeposited metals on which indium can be electrolytically deposited and in which minute pin holes occur. Likewise, in the plating :of fine wire-drawing dies by use of this bath, for example a die with a 0.08 inch opening, a uniform plate was obtained over the entire die surface, notwithstanding the deep and narrow opening.

The articles to be plated may be prepared for treatment the usual way, but since the'bathas described abovei-s chemically neutral (pl-l1 plus or minus :02) no corrosive action occurred, and tor the same reason preliminary cleaningof the work is more impoittant than in more corrosive baths. I I 1 Thebathis substantially self-maintaining over prolongedperiods of use, the indium going into the solution from the anode as it is deposited at the cathode. Insofar as losses occur by leakage, evaporation or by carrying over on the work, these may be made up by adding pure formamide. Once the bath is in operation such additional indium as may be necessary to balance the added formamide is made available from the anode.

Although, as indicated above, addition agents may be used as desired by, and within the skill of, the practical platers who may use the invention, it is an advantage of the invention that the simple bath as indicated above is satisfactory without other additions.

The indium hydroxide is added to the forrnamide in the proportion indicated and heated for two hours at a temperature of about C. to about C., whereupon the indium hydroxide goes into solution.

Other indium compounds, particularly salts of weak acids such as indium formate, indium sulfamate, etc., may be used, the anion in such case, of course, being one which is not objectionable in the plating solution or which will precipitate or separate from solution. In the case of indium sulfamate, for example, a pre cipitate is formed which should be filtered from the solution before it is used. In the case of indium formate, it may be decomposed by heating to 200 C. with evolution of CO2 and H2. It is an important advantage of the present inven tion that the hydroxide can be used, thus avoid-- ing possible objection from the presence of other anions or the corresponding acid.

A similar advantage can, of course, be obtained by producing the indium formamide, e. g. by reaction of indium hydroxide and formamide, as described above, and subsequent separation by distillation, and the resulting product added instead of indium hydroxide. Ordinarily, however, there is little advantage to be gained which would vjustify additional expense of such a procedure.

by indium hydroxide with the proportions indilocated. With more acid salts of indium or with acid addition agents, the pH may be further reduced and by the addition of stronger amines or other basic reacting addition agents, the pH may be increased.

The proportion of the indium compound indicated is not critical. Thus satisfactory plat me can be effected with from 10 to 45 or even as high as 100 grams per liter of indium hydroxide in formamlde.

I claim:

1. A bath for electrolytic deposition of indium which consists essentially of asolution resulting from dissolving indium hydroxide in formamide, said solution having a concentration of from 10 to 100 grams per liter of indium hydroxide in formamide. l

2. A bath for electrolytic deposition of indium which consists essentially of a solution resulting from dissolving indium hydroxide in formamide, said solution being of pH approximately '7 and having a concentration of from 10 to 100 grams per liter of indium hydroxide in formamide.

3. The method for electrolytic deposition of indium which consists essentially of preparing a bath consisting of indium hydroxide in formamide in an amount between 10 and 100 grams per liter of indium hydroxide in formamide, placing in contact with the resulting solution as a cathode an article on the surface of which indium can be electro-deposited, placing an indium anode in contact with said solution, and passing an electric current from said anode to said cathode through said solution to electrolytically deposit indium on the surface of said article.

4. A method as in claim 3 wherein formamide is added to said solution to make up for losses occurring during the electrodeposition.

JOHN ROBERT DYER, JR.

REFERENCES CITED -The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Smart July 8, 1947 OTHER REFERENCES Number 

